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HID
High Impedance Differential Module

Use the HID module in conjunction with a high-speed overcurrent relay to provide three phase high impedance differential protection for substation busbars of any voltage level. Additionally, it can also be used to protect electrical machines like transformers, generators or motors against restricted ground faults.

Each HID module includes resistors that provide the associated high impedance relay with stability againstexternal faults, and varistors (MOV - Metal Oxide Varistors) in order to limit the secondary peak voltage below 2 kV during fault conditions.

Use the auxiliary contacts provided by an optional latching relay to short-circuit the resistors once the associated relay has tripped, to prevent the fault current from circulating through the resistors.

The HID front panel incorporates a Reset pushbutton to reset the latching relay once the fault has been cleared, in order to eliminatethe resistors short circuit.

Features & Benefits:

  • Single-zone bus protection, reactor protection, or sensitive restricted earth fault protection on grounded, wye-connected power transformer windings
  • Provides metal oxide varistors (MOV) to clamp secondary peak voltage to less than 2 kV

Applications

  • Single-zone bus protection, reactor protection, or sensitive restricted earth fault protection on grounded, wye-connected power transformer windings
  • High impedance differential protection for electrical machines such as generators or motors, including lockout logic.

Protection & Control

  • The combination of HID module with a high-speed overcurrent relay can be applied for bus protection in most cases where CTs having negligible leakage reactance are used.
  • Additional functionality provided by the additional overcurrent device includes:
    • time stamped sequence of event recorder
    • waveform capture
    • data logger
    • communication to remote control centers